jQuery.fn.floatdiv = function(location) {
	// 判断浏览器版本
	var isIE6 = false;
	var Sys = {};
	var ua = navigator.userAgent.toLowerCase();
	var s;
	(s = ua.match(/msie ([\d.]+)/)) ? Sys.ie = s[1] : 0;
	if (Sys.ie && Sys.ie == "6.0") {
		isIE6 = true;
	}
	var windowWidth, windowHeight;// 窗口的高和宽
	// 取得窗口的高和宽
	if (self.innerHeight) {
		windowWidth = self.innerWidth;
		windowHeight = self.innerHeight;
	} else if (document.documentElement
			&& document.documentElement.clientHeight) {
		windowWidth = document.documentElement.clientWidth;
		windowHeight = document.documentElement.clientHeight;
	} else if (document.body) {
		windowWidth = document.body.clientWidth;
		windowHeight = document.body.clientHeight;
	}
	return this
			.each(function() {
				var loc;// 层的绝对定位位置
				var wrap = $("<div></div>");
				var top = -1;
				if (location == undefined || location.constructor == String) {
					switch (location) {
					case ("rightbottom"):// 右下角
						loc = {
							right : "0px",
							bottom : "0px"
						};
						break;
					case ("leftbottom"):// 左下角
						loc = {
							left : "0px",
							bottom : "0px"
						};
						break;
					case ("lefttop"):// 左上角
						loc = {
							left : "0px",
							top : "0px"
						};
						top = 0;
						break;
					case ("righttop"):// 右上角
						loc = {
							right : "0px",
							top : "0px"
						};
						top = 0;
						break;
					case ("middletop"):// 居中置顶
						loc = {
							left : windowWidth / 2 - $(this).width() / 2 + "px",
							top : "0px"
						};
						top = 0;
						break;
					case ("middlebottom"):// 居中置低
						loc = {
							left : windowWidth / 2 - $(this).width() / 2 + "px",
							bottom : "0px"
						};
						break;
					case ("leftmiddle"):// 左边居中
						loc = {
							left : "0px",
							top : windowHeight / 2 - $(this).height() / 2
									+ "px"
						};
						top = windowHeight / 2 - $(this).height() / 2;
						break;
					case ("rightmiddle"):// 右边居中
						loc = {
							right : "0px",
							top : windowHeight / 2 - $(this).height() / 2
									+ "px"
						};
						top = windowHeight / 2 - $(this).height() / 2;
						break;
					case ("middle"):// 居中
						var l = 0;// 居左
						var t = 0;// 居上
						l = windowWidth / 2 - $(this).width() / 2;
						t = windowHeight / 2 - $(this).height() / 2;
						top = t;
						loc = {
							left : l + "px",
							top : t + "px"
						};
						break;
					default:// 默认为右下角
						location = "rightbottom";
						loc = {
							right : "0px",
							bottom : "0px"
						};
						break;
					}
				} else {
					loc = location;
					alert(loc.bottom);
					var str = loc.top;
					// 09-11-5修改：加上top为空值时的判断
					if (typeof (str) != 'undefined') {
						str = str.replace("px", "");
						top = str;
					}
				}
				/* fied ie6 css hack */
				if (isIE6) {
					if (top >= 0) {
						wrap = $("<div style=\"top:expression(documentElement.scrollTop+"
								+ top + ");\"></div>");
					} else {
						wrap = $("<div style=\"top:expression(documentElement.scrollTop+documentElement.clientHeight-this.offsetHeight);\"></div>");
					}
				}
				$("body").append(wrap);

				wrap.css(loc).css({
					position : "fixed",
					z_index : "999"
				});
				if (isIE6) {

					wrap.css("position", "absolute");
					// 没有加这个的话，ie6使用表达式时就会发现跳动现象
					// 至于为什么要加这个，还有为什么要加nothing.txt这个，偶也不知道，希望知道的同学可以告诉我
					$("body").css("background-attachment", "fixed").css(
							"background-image", "url(n1othing.txt)");
				}
				// 将要固定的层添加到固定层里
				$(this).appendTo(wrap);
			});
};